Ester based lubricant composition containing phenothiazine and aminoquinoline



3,038,859 ESTER BASED LUBRICANT COMPOSITION CON- gllggit} PHENOTHIAZINE AND AMINOQUIN- Daniel B. Eickemeyer and Elwin B. Ovist, Park Forest, 111., assignors to Sinclair Refining Company, New York, N.Y., a corporation of Maine No Drawing. Filed June 24, 1959, Ser. No. 822,449 Claims. (Cl. 252-47) This iilvention relates to an ester-based lubricant composition" and more particularly to ester-based lubricant compositions containing phenothiazine and aminoquinoline which are effective as corrosion inhibitors or antioxidants.

Organic compounds, such as lubricating oils, undergo oxidation upon exposure to air. This process is accentuated by elevated temperatures such as occur in engines and other operating machinery. When such organic compositions are used as motor or machinery lubricants, their stability is still further drastically reduced due to their contact with metal surfaces which give up metallic particles into the lubricant. Such abraded or dissolved metals or metal salts appear to act as oxidation catalysts in the lubricant causing the formation of primary oxidation products which in turn cause further degradation of the organic compounds present in the composition. In addition, water also causes corrosion of metallic surfaces and accentuates oxidation of the lubricant. Problems of this nature are encountered in mineral oils but appear to be particularly troublesome in synthetic oleaginous fluids exemplified by esters.

Numerous oxidation and corrosion inhibitors have been found for use in lubricating compositions and many combinations thereof also have been tested. In many instances the effect of such combination is merely the additive effect of each of the inhibitors employed but in other cases a greater effect is exhibited by the additives used, thus promoting to an unaccountable degree the oxidation and corrosion protection of the composition.

It is the particular object of the invention to provide an ester oil of lubricating viscosity having the superior lubricant gproperties characteristic of the synthetic diester oils, and thoroughly inhibited with respect to oxidation deterioration. Further, the additives of this invention have proven to be effective in retarding sludge formation in synthetic ester lubricants which are exposed to high temperatures, and also have proven far more effective than the conventional use of phenothiazine alone in retarding sludge formation in ester fluids made from a branched neostructured alcohol component.

The present invention provides an improved synthetic ester-based lubricant composition containing phenothiazine and aminoquinoline so as to exhibit increased resistance to oxidation under high temperatures such as in excess of 400 F.

The preferred compound utilized in this invention is 3-arninoquinoline and its ring substituted alkyl derivatives. The aminoquinoline may be added in amounts from about .01 to 5 percent by weight of final composition with a preferred amount of from about .1 to 2 percent by Weight of final composition. This additive is normally added to the ester-based lubricant along with the phenothiazine. The phenothiazine is normally present in amounts from about .01 to 5 percent by Weight of final composition with a preferred amount being from about .1 to 2 percent and the phenothiazine may be substituted with alkyl groups. The--relative concentrations of the additives will vary With the particular ester lubricant employed and also dependent upon the characteristics of the final lubricant composition desired. Normally, it is preferred that the 3,038,859 Patented June 12, 1962 I 'ice 3-aminoquinoline to phenothiazine molar ratio should be at least about 1 to 1 or greater.

The lubricant composition of this invention includes as the major compound a base oil which is an ester of lubricating viscosity which may be, for instance, a simple ester or compounds having multiple ester groupings such as complex esters, polyesters, or diesters. These esters are made from monoand polyfunctional aliphatic alcohols and aliphaticcarboxylic acids, frequently of about 4 to 12v carbon atoms. The reaction product of a {HD1101 functional alcohol and a monocarboxylic acid is usually considered to be a simple ester. A diester is usually considered to be the reaction product of 1 mole of a dicarboxylic acid, say of 6 to 10 carbon atoms, with 2 moles of a monohydric alcohol or of 1 mole of a glycol of 4 to 10 carbon atoms with two moles of a moncarboxylic acid of 4 to 10 carbon atoms. The diesters frequently contain from 20 to 40 carbon atoms. A complex ester is usually considered to be of the type XYZY-X in which X represents a monoalcohol residue, Y represents a dicarboxylic'acid residue and Z represents a glycol residue and the linkages are ester linkages. Those esters, wherein'X represents a monoacid residue, Y represents a glycol residue and Z represents a dibasic acid residue are also considered to be complex esters. The complex esters often have 30 to 50 carbon atoms. Polyesters, or polyester bright stocks can be prepared by direct esterification of dibasic acids with glycols in about equimolar quantities. The polyesterification reaction is usually continued until the product has a kinematic viscosity from about 15 to 200 centistokes at 210 F., and preferably 40 to centistokes at 210 F.

Although each of these products in itself is useful as a lubricant, they are particularly useful when added or blended With each other in synthetic lubricant compositions. These esters and blends have been found to be especially adaptable to the conditions to which turbine engines are exposed, since they can be formulated to give a desirable combination of high flash point, low pour point, and high viscosity at elevated temperatures, and need contain no additives which might leave a residue upon volatilization. In addition, many complex' esters have shown good stability to shear. Natural esters, such as castor oil may also be included in the blends, as may be up to about 1 percent or more by weight of a foam inhibitor such as a methyl silicone polymer or other additives to provide a particular characteristic, for instance, extreme pressure or load carrying agents, corrosion inhibitors, etc., can be added.

Typical synthetic lubricants may be formulated essentially from a major amount (about 6085%) of a complex ester and a minor amount (about 15-40%) of a diester, by stirring together a quantiy of diester and complex ester at an elevated temperature, altering the proportions of each component until the desired viscosity is reached. Polyesters can be employed to thicken diester base stocks to increase the load carrying capacity of the base diester oil. The polyester will generally not comprise more than about 50 Weight percent of the blend, preferably about 20 to 35 Weight percent. Usually the amount of the polyester employed in any blend would be at least about 5 percent, and the majority of the lubricant is a diester. Advantageously the final lubricating oil composition would have a maximum viscosity at 40 F. of about 13,000 centistokes and a minimum viscosity of about 7.5 centistokes at 210 F.

The monohydric alcohols employed in these esters usually contain less than about 20 carbon atoms and are generally aliphatic. Preferably the alcohol contains up to about 12 carbon atoms. Useful aliphatic alcohols include butyl, hexyl, methyl, iso-octyl, and dodecyl alcohols,

' diol.

C oxo alcohols and octadecyl alcohols. C to C branched chain primary alcohols are frequently used to improve the low temperature viscosity of the finished lubricant composition. Alcohols such as n-decanol, Z-ethylhexanol, x0 alcohols, prepared by the reaction of carbon monoxide and hydrogen upon the olefins obtainable from petroleum products such as diisobutylene and C olefins, ether alcohols such as butyl carbitol, tripropylene I glycol mono-isopropyl ether, dipropylene glycol monohexanol; 4.3% ot-alkyl alkanols and other materials.

Generally, the glycols contain from about 4 to 12 carbon atoms; however, if desired they could contain a greater number. Among the specific glycols which can be employed are 2-ethyl-1,3-hexanediol, 2-propyl-3,3-heptanediol, 2-methyl-l,3-pentanediol, 2-butyl-1,3-butanediol, 2, 4-diphenyl-l,B-butanediol, and 2,4-dimesityl-1.,3-butane- In addition to these glycols, ether glycols may be used, for instance, where the alkylene radical contains 2 to 4 carbon atoms such as diethylene glycol, dipropylene glycol and ether glycols up to 1000 to 2000 molecular weight. The most popular glycols for the manufacture of ester lubricants appear to be polypropylene glycols having a molecular weight of about 100-300 and 2-ethyl hexanediol. The 2,2-dimethyl glycols, such as neopentyl glycol have been shown to impart heat stability to the final blends. Minor amounts of other glycols or other materials can be present as long as the desired properties of the product are not unduly deleteriously afifected. Aside from glycols, the esters may be made from polyhydric alcohols of more than two hydroxyl groups, e.g. pentaerythritol, trimethylolpropane and the like.

Preferred monocarboxylic acids are those of 8 to 24 carbon atoms such as stearic, lauric, etc. The carboxylic acids employed in making ester lubricants will in general contain from about 4 to 12 carbon atoms. Suitable acids are described in US. Patent No. 2,575,195 and include the aliphatic dibasic acids of branched or straight chain structures which are saturated or unsaturated. The preferred acids are the saturated aliphatic carboxylic acids containing not more than about 12 carbon atoms, and mixtures of these acids. Such acids include succinic, adipic, suberic, azelaic, and sebacic acids and isosebacic acid which is a mixture of a-ethyl suberic acid, a,a-diethyl adipic acid and sebacic acid. This composite of acids is attractive from the viewpoint of economy and availability since it is made from petroleum hydrocarbons rather than the natural oils and fats which are used in the manufacture of many other dicarboxylic acids, which natural oils and fats are frequently in short supply. The preferred dibasic acids are sebacic and azelaic or mixtures thereof. Minor amounts of adipic used with a major amount of sebacic may also be used with advantage.

Various useful ester base oils are disclosed in United States Patents Nos. 2,499,983, 2,499,984, 2,575,195, 2,575,196, 2,703,811, 2,705,724 and 2,723,286. Generally, the synthetic base oils consist essentially of carbon, hydrogen and oxygen, i.e. the essential nuclear chemical structure is formed by these elements alone. However, these oils may be substitutedwith other elements such as halogens, e.g. chlorine and fluorine. Some representative components of ester lubricants are ethyl palmitate, ethyl stearate, di-(2-ethylhexyl) sebacate, ethylene glycol di- The cut which makes I laurate, di-(Z-ethylhexyl) phthalate, di-(l,3-methyl butyl) adipate, di-(Z-ethyl butyl) adipate, di-(1-ethy1 propyl) adipate, dicthyl oxylate, glycerol tri-n-octoate, di-cyclohexyl adipate, di(undecyl) sebacate, tetraethylene glycoldi-(Z-ethylene hcxoate), di Cellosolve phthalate, butyl phthallyl butyl glycolate, di-n-hexyl fumarate polymer, dibenzyl sebacate, and diethylene glycol -bis(2-n-butoxy ethyl carbonate). 2-ethylhexyl-adipate-neopentyl glycyladipate-Z-ethylhexyl, is a representative complex ester. Generally, these synthetic ester lubricants have a viscosity ranging from light to heavy oils, e.g. about 50 SUS at F. to 250 SUS at 210 F., and preferably 30 to SUS at 210 F.

The esters are manufactured, in general, by mere reaction of, the alcoholic and acidic constituents, although simple esters may be converted to longer chain components by transesterification. The constituents, in the proportions suitable forgiving the desired ester, are reacted preferably in the presence of a catalyst and solvent or water entraining agent to insure maintenance of the liquid state during the reaction. Aromatic hydrocarbons such as xylene or toluene have proven satisfactory as solvents. The choice of solventintluences the choice of temperature at which the esterification is conducted; for instance, when toluene is used, a temperature of 140 C. is recommended; with xylene, temperatures up to about 195 C. may be used. To provide a better reaction rate an acid esterification catalyst is often used. Many of these catalysts are known and include, for instance, HCl, H 80 NaHSO aliphatic and aromatic sulfonic acids, phosphoric acid, hydrobromic acid, HF and dihydroxyfluoboric acid. Other catalysts are thionyl chloride, boron trifiuoride, and silicon tetrafiuoride. Titanium esters also made valuable esterification and transesterification catalysts.

In a preferred reaction, about 0.5 to about 1 weight percent, or advantageously, 0.2 to 0.5% of the catalyst is used with a xylene solvent at a temperature of to 200 C. while refluxing water. The temperatures of the reaction must be sufiicient to remove the water from the esterification mass as it is formed. This temperature i usually at least about 140 C. but not so high as to decompose the wanted product. The highest temperature needed for the reaction will probably be about 200 C-, preferably not over about C. The pressure is conveniently about atmospheric. Although reduced pressure or superatmospheric pressure could be utilized, there is usually no necessity to use reduced pressures, as the temperatures required at atmospheric pressure to remove the Water formed do not usually unduly degrade the product.

When reacting glycols with dibasic acids to produce a polyester, it is preferred to continue the reaction with concomitant boiling off of Water from the reaction mixture until the polyester product has a kinematic viscosity of about 15 to 200 centistokes at 210 F., preferably about 40 to 130 centistokes. When this point has been reached, the polymerization can be stopped, for instance, by adding a capping alcohol to the reaction mixture, and continuing to reflux until water ceases to be evolved. The capping alcohol is a low molecular weight mono-alcohol of up to about 20 carbon atoms. It is standard practice, when esters are made using the conventional acid catalysts such as sodium 'bisulfate or paratoluenesulfonic acid to give the esters an after-treat by washing the ester with a 5 percent aqueous K CO solution or by heating the ester in an autoclave for 15 hours at 340 to 350 F. with 10 weight percent of propylene oxide. It is also conventional to subject the ester to filtration to remove insoluble materials. After this the product may be subjected to a reduced pressure distillation or stripping at 100 to 200 C. to remove volatile materials, such as water, the solvent, and light ends.

Samples of ester fluids without an oxidation inhibitor and samples containing phenothiazine, 3-aminoquinoline alone and samples made according to the present invention containing varying portions of phenothiazine and 3- aminoquinoline are shown in the results of oxygen-adsorption tests at 450 F. The tests were conducted by passing a stream of oxygen at the rate of one cubic foot per hour through 75 gms. of the ester fluid containing the inhibitors and comparing the amount of oxygen adsorbed vs. time. The induction period is the time in which little or no oxygen is adsonbed by the fluid. The end of the induction period is signaled by a marked increase in the rate of oxygen adsorption. The results of these tests are shown in Table I.

1 n-C1 acid-pentaerythritol ester. It has the following inspection data: acid No. 0.01, sap No. 400, vis. at 212 F., 5.30 05., vis. at 100 F.,

2 The test was stopped at this point. The end of the induction period had not been reached, however.

The induction period serves as a significant measure of the relative effectiveness of the inhibitors. As shown in the table, the 3-aminoquinoline-phenothiazine synthetic ester based lubricant composition prevents oxygen uptake by the fluid by more than twice as long as does phenothiazine alone and also more than twice as long as would be expected from the results obtained when using 3-aminoquinoline and phenothiazine alone.

We claim:

1. A lubricant composition consisting essentially of an ester based synthetic fluid of lubricating viscosity, about 0.01 to 5% by weight phenothiazine and about 0.01 to 5% by Weight aminoquinoline and effective to retard oxidation of said ester based synthetic fluid at temperatures in excess of 400 F., said estenbased synthetic fluid being of an ester of an alcohol of 4 to 12 carbon atoms and a carboxylic acid of 4 to 12 carbon atoms.

2. The lubricant composition of claim 1 where aminoquinoline is 3-aminoquinoline.

3. The lubricant composition of claim 1 wherein the alcohol and carboxylic acid of 4 to 12 carbon atoms are aliphatic.

4. The lubricant composition of claim 2 containing about .1 to 2 percent by weight of final composition of phenothiazine.

5. The lubricant composition of claim 4 containing about .1 to 2 percent by weight of final composition of S-aminoquinoline.

6. The lubricant composition of claim 3 wherein the carboxylic acid of 4 to 12 carbon atoms is selected from the group consisting of aliphatic monocarboxylic acids and aliphatic dicarboxylic acids.

7. The lubricant composition of claim 6 wherein the aliphatic alcohol of 4 to 12 carbon atoms has no hydrogen on a beta carbon atom.

8. The lubricant composition of claim 6 wherein the ratio of aminoquinoline to phenothiazine is at least about 1:1.

9. The lubricant composition of claim 6 whereinthe aliphatic alcohol of 4 to 12 carbon atoms has no hydrogen on a beta carbon atom and the ratio of aminoquinoline to phenothiazine is at least about 1:1.

10. The lubricant composition of claim 9 wherein the aminoquinoline is 3-aminoquinoline.

References Cited in the file of this patent UNITED STATES PATENTS Dietrich Apr. 30, 1940 Musher Oct. 1, 1940 Blake etal. June 2, 1959 OTHER REFERENCES 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF AN ESTER-BASED SYNTHETIC FLUID OF LUBRICATING VISCOSITY, ABOUT 0.01 TO 5% BY WEIGHT PHENOTHIAZINE AND ABOUT 0.01 TO 5% BY WEIGHT AMINOQUINOLINE AND EFFECTIVE TO RETARD OXIDATION OF SAID ESTER BASED SYNTHETIC FLUID AT TEMPERATURES IN EXCESS OF 400*F., SAID ESTER-BASED SYNTHETIC FLUID BEING OF AN ESTER OF AN ALCOHOL OF 4 TO 12 CARBON ATOMS AND A CARBOXYLIC ACID OF 4 TO 12 CARBON ATOMS. 